BROWN NODDY CHICK PREDATION BY GREAT FRIGATEBIRDS IN THE NORTHWESTERNHAWAIIAN-ISLANDS

Adult female Great Frigatebirds (Fregata minor) were responsible for 6 4% of the predatory behaviors on Brown Noddy (Anous stolidus) chicks o n Tern Island, French Frigate Shoals, Hawaii. Subadults with red orbit al rings (presumably females) also preyed on Brown Noddy chicks, altho ugh they were observed hunting less frequently than adult females. No adult male frigatebirds were observed hunting in 118,3 hours of observ ation. Frigatebird predation likely accounted for 95% of mortality obs erved in Brown Noddy chicks less than 24 days of age. Chicks were as l ikely to survive to hedging regardless of nest location or down colora tion; however, more chicks survived to fledging if hatched between mid -February and mid-May. Unequal sex ratios, sexual size dimorphism, res ource partitioning, and breeding strategies of frigatebirds were evalu ated to explain why sex differences in frigatebird predation behaviors were observed on Tern island.